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Old 11th December 2011, 05:54 PM   #1
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Default compund motor subwoofer

i have some midfi unmarked 10 inch subwoofer. play pretty well in ported design but at moderate levels. i am making an experiment for lineartity and greater power handling by improving BL curve linearity and dual spider.

Basically the idea is from compound puu push /isobarick subwoofer loading. The idea is to take it further from here. As we know that in ideal isobarik loading there is non linearity in trapped air, Vas is halfed so is 3db loss inefficiency. Lower distortion one motor is pushing while other pulling, the BL curve gets symettrical.

I intend to remove the surround and cone of one woofer , now i would have one motor with voice coil and basket. Invert it on top of the second woofer , bolt the two bakets together and connect the voicee coils with PVC pipe of the size of the voice coil i.e 3 inch with lenght of exact space between then glue them terogether.

Now both motors and two coils oare physically connceted in pull-push mehtod, BL curve non linearity is corrected and so is spider. A variation is like this

But obviously it would have one cone , one surround, two motors , two coils. Now my question:

Since one surround and cone is removed its compliance would be altered, would it introduce any distorition ? Fs would vary ?

Xmax would not increase i know but i am aiming at SQ here. suggestions please pictures to follow quickly.
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File Type: jpg 12sub.jpg (73.1 KB, 167 views)
File Type: jpg 1%20cone%20expld.jpg (65.1 KB, 160 views)
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Old 11th December 2011, 06:01 PM   #2
badman is offline badman  United States
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Have you reviewed JBL's Differential drive? Worth looking over given your experimentation.

On your prototype, I'd cut some windows out of the enclosed spider sub-assembly for further ventilation, since you're going to all this trouble. Also, I'd want to use shorting rings and extended poles to give a head-start on the low distortion part.

Will be interesting to see where this takes you!
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Old 11th December 2011, 06:18 PM   #3
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something like this:
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Old 11th December 2011, 06:30 PM   #4
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better this one.
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Old 11th December 2011, 06:45 PM   #5
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EVEN more dtailed.
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Old 11th December 2011, 07:43 PM   #6
epa is offline epa  Netherlands
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nice experiment,i like it.
i think the hole moving asambly should be in ballance ,i think a pvc pipe would become to heavy compared to the cone,but who knows.
the added weight of the extra voice coil and suspension wil lower fs already.
maybe try something lighter to connect the coils,paper maybe.
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Old 11th December 2011, 07:58 PM   #7
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I'm pretty sure this has already been done. Co-Drive I think it was called.
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Old 11th December 2011, 08:15 PM   #8
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The differetial is different. it uses 3 stacked magnets and two coils on a single former to maintian linearity of BL curve , symmetr but no uniformity, secondly the spider and nno linearlity in both directions as well as control over lateral movements in my design..

I think its a good idea for DIY and not commercially viable for looks and odd intallation, and i think going to loose some SD as cone centre would be locked outiwth PVC pipe. Again it would be running i series to ensure same current through both coils.

Any guess on Fs, Vas and Qts, Qms, Qes. ??? and SQQQQ
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Old 11th December 2011, 08:18 PM   #9
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Co-Drive is the first figure. its different. see the last post picture. However is one way of doing too difficult. This can be done by removing , one surround, inverting the subwoofer and just paste it un-amended woofer, or remove the cone as well and connect the first woofer VC with a light pipe to the second woofer.
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Old 12th December 2011, 01:20 AM   #10
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You can simulate this in AkAbak. I think you will find that it will perform slightly better than a standard "isobaric" configuration, but probably not enough better to make it worth the effort.

I used AkAbak to compare a "standard" isobaric (2 drivers mounted face to face, thus a small air compliance between them) with a "rigid" isobaric (no compliance between them). The overall performance was almost unchanged, but there was a difference in excursion between the two drivers in the "standard" isobaric configuration.
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